Fifty years ago, residents here witnessed a scene which has led them to harbour a secret – one which throws new light on the death of former United Nations secretary-general Dag Hammarskjöld, who was en route to negotiations to address civil unrest in Congo,

The official explanation for Hammarskjöld's crash outside Ndola airport on the evening of 17 September 1961 was pilot error. But accounts from local people living near the airport in Chifubu or from charcoal makers out in the bush where the crash happened, were never heard.

Among the market pathways, freshly cut planks of wood loaded onto bicycle-pulled trailers trundle through the chaos, balanced by four or five young men. Wood cutting is big business here, the planks are bought from local sawmills and turned into furniture or used to construct houses.

Away from the bustle of the market, set behind some trees, Safeli Mulenga sits outside his house. He is tall and thin, and not very well, but slowly he gets up and walks into a sitting room decorated with framed pictures of himself and his family.

He sits down on a large brown sofa and smiles gently before recounting that evening in September when he saw Hammarskjöld's plane crash.

At about 8pm, on its third round, fire was thrown onto the plane from somewhere above it, he said.

Although Mulenga didn't know that the plane was carrying Hammarskjöld, a peace broker with a reputation for protecting countries such as Zambia against the great powers, he soon found out.

But he never mentioned what he had seen, because the federal government didn't want anybody to know, he said. Some people were taken away after talking about the crash. When they returned, they never spoke about the incident again, he said sadly, looking down at the floor.

"At the time there was a political atmosphere. It was a bad moment for us because we thought that Dag Hammarskjöld had just come to help in the struggle for freedom. The man who had come to help in political liberation had died."